i've found that the little rena 2" diffusers do a good job of maintaining a
small bubble size over an extended period. i've tried several other
"airstones" as well as limewood diffusers and they all seem to generate
large bubbles from the start or soon thereafter.

when i say small i mean bubbles small enough that 70% (approximately)
disappear within 8" of water column. with a 75G i don't think anything would
make it to the top if the diffuser was at the bottom.

if you use the rena make sure to trim the lip of the rubber at the top
otherwise it will collect the fine bubbles into larger ones.

jtm

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"LeighMo" wrote in message
...
Possibly a bigger issue with the Dave Gomberg high pressure system, if
it's the same as when I bought mine several years ago, is that the
tiny little Eheim diffusor isn't very effective in large tanks.

It's fine in my 75 gallon. I believe Chuck uses a wet-dry filter, which
tends
to lose a lot of CO2. The Eheim will probably be fine with any "normal"
filter.

I am considering switching to some kind of reactor, or injecting directly
into
the filter intake, in hopes of lowering the maintenance required. You do
have
to rinse the Eheim diffusor's ceramic disk every week or two, to keep the
CO2
bubble size small.


Leigh

http://www.fortunecity.com/lavender/halloween/881/